1. Field of the Invention
This invention relates to cutters for sheet material and, more particularly, to a sheet cutter having a separable blade assembly.
2. Background Art
A myriad of different cutters for sheet material are currently available on the market. Among the many uses for these cutters are the trimming of photographs, cutting of plain papers and light cardboard, etc. One popular design used for this purpose has a base with a flat surface for supporting the sheet material to be cut and a rail assembly which overlies the base support surface. The rail assembly has a flat surface which faces the base support surface. Between the rail assembly and base support surfaces, a space is defined within which the sheet material to be cut is situated. A blade assembly is mounted to the rail assembly for guided movement in a linear cutting path.
An exemplary structure having this design is shown in U.S. Pat. No. 5,671,647, assigned to Carl Manufacturing Co., Ltd. In this particular device, the rail assembly has spaced rail portions which define a guide slot for the blade assembly. Each rail portion has an edge which bounds the slot. The blade assembly has spaced, oppositely opening, U-shaped receptacles to engage, one each, with a rail edge. Each U-shaped receptacle is bounded by upwardly and downwardly facing surfaces to confine vertical movement of the edges therewithin.
In one version of this cutter, the blade assembly and rail assembly are designed so that the blade assembly can be placed relative to the rail assembly selectively in a) an operative state and b) a separated state, with the latter facilitating replacement or repair of the blade assembly. With the blade assembly in the operative state, the rail portion edges reside within the first and second receptacles so that the blade assembly is guided in the cutting path by the rail assembly. The orientation of the blade assembly relative to the rail assembly is maintained by the interaction of the rail portions with base surfaces bounding each of the U-shaped first and second receptacles. These base portions have a sufficient length to resist skewing of the blade assembly during operation.
To place the blade assembly in its separated state, the spacing between the edges of the rail portions must be increased sufficiently to allow the rail portion edges to be withdrawn from both the first and second receptacles on the blade assembly. In one commercial version, separation is effected by having the user grasp the blade assembly, as between the fingers, and manually exert a force sufficient to wedge the rails apart. This action can be assisted by drawing the blade assembly with one hand and producing a separating force on the rail portions with the other. Since the blade assemblies are generally quite small, they generally do not lend themselves to being positively grasped to effect extraction of the blade assembly from the rail assembly guide slot. This may lead to situations where the blade assembly ultimately springs from the slot, as a result of which it might have to be recovered by the operator. Alternatively, during the extraction process, the blade assembly may reorient so that the cutting blade undesirably becomes exposed to the user. This same problem is potentially encountered as the separated blade assembly is pressed against the rail portions to effect installation thereof.
Designers of these cutting devices generally anticipate that users will wish to simultaneously cut multiple sheets of material. In U.S. Pat. No. 5,671,647, a construction is disclosed wherein the rail assembly is flexible so that it can be pressed towards the base support surface to squeeze different numbers of layers of the captive sheet material to maintain the same fixedly in a desired location during the cutting operation. This captive force is increased and maintained by exerting a force on the rail assembly through the blade assembly as the cutting operation is carried out.
One potential problem with cutting apparatus of this type is that, while the sheet material may be positively held for a true cut, the blade assembly is prone to deviating from its intended path. This is a problem that may be introduced by making the blade assembly separable from the rail assembly, as described above. The flexibility built into the rail portions, which permits them to be moved apart to allow the blade assembly to be extracted, inherently introduces the opportunity for the blade to shift off its intended linear path. This problem can be addressed by making the rail portions more rigid. However, this inherently makes the blade removal and assembly processes more difficult. Consequently, it has been common to make the rail portions less than optimally rigid to facilitate blade assembly, separation, and reinstallation. As a result, some of the desired accuracy may be forfeited, particularly when multiple layers of sheet material are being cut and a greater advancing force is being applied by the operator to the blade assembly.